Kepler finds clouds on extrasolar planet

"How's the weather?" has just become a topic of interstellar conversation. Using data from NASA's Kepler and Spitzer space telescopes, astronomers have mapped the first clouds discovered on an extrasolar planet. Not only does this technique give us an interesting bit of pure science, it could also be applied in the search for more earth-like planets according to NASA.

The analysis of the data collected by Kepler (before it suffered an irreparable reaction wheel failure) goes beyond looking for planets outside the Solar System as scientists seek to learn more about their nature.

The map shows clouds on the exoplanet Kepler-7b, one of the first five planets confirmed discovered by the unmanned Kepler probe. Circling Kepler-7, this planet is classified as a "hot Jupiter." It's 1.5 times the size of Jupiter, though it's less than half its mass and has very low gravity. Small wonder some scientists have described it as "puffy."

With the second lowest density of any known exoplanet, Kepler-7b orbits 0.06 AU (5.5 million mi / 8.9 million km) from its star in a year equal to five Earth days. The estimated temperature of Kepler-7b is between 1,500⁰ and 1,800⁰ F (800⁰ and 1,000⁰ C). This is relatively cool for a planet so near its star and, in addition, Kepler-7b has a very high albedo.

While the planet's atmosphere was found to be hot to a very great depth, the relatively cool temperature indicates that the light was bouncing off high clouds on the western hemisphere with clear skies in the east. It's not very balmy however, given that it's twice the temperature needed to melt lead and that, since it has a silicate-based cloud composition, it rains glass.

"Kepler-7b reflects much more light than most giant planets we've found, which we attribute to clouds in the upper atmosphere," say Thomas Barclay, Kepler scientist at NASA's Ames Research Center in Moffett Field, California. "Unlike those on Earth, the cloud patterns on this planet do not seem to change much over time – it has a remarkably stable climate."

Kepler discovered Kepler-7b by measuring light intensity of stars as possible planets pass in front of them. Sudden dips indicate that a planet may be present. However, the resolution of Kepler meant that by studying the light curve of the planet in detail as it went through moon-like phases, it saw a bright spot on the planet’s map. Unfortunately, it couldn't make out if this was light reflected off of clouds or a hot spot.

Artist's impression of the Spitzer space telescope (Image: NASA)

This is where Spitzer came in. This NASA space telescope works in infrared at different wavelengths than Kepler, which allows it to eliminate alternatives, such as a hot spot and confirm that clouds are the most likely explanation.

"By observing this planet with Spitzer and Kepler for more than three years, we were able to produce a very low-resolution 'map' of this giant, gaseous planet," says Brice-Olivier Demory of Massachusetts Institute of Technology in Cambridge. "We wouldn't expect to see oceans or continents on this type of world, but we detected a clear, reflective signature that we interpreted as clouds."